STUDIES ON THE PAIN-SENSIBILITY OF ARTERIES

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Abstract
I. Injection of irritants into arteries of amytalized animals [Exps. chiefly on cats, with a few on dogs] results in pseudaffective reactions indicating stimulation of afferent neurones subserving pain-sensation. This sensibility exists independent of stretching or spasm of arterial muscle and is shown to be conditioned by chemical stimulation of nerve-endings located about the finer arterial branches. It is believed that pain arising from manipulation of arteries is entirely a result of trauma to accompanying nerve trunks, and, likewise, that much of the pain which accompanies surgical procedures results from trauma to nerve-trunks rather than stimulation of terminal receptors. Spasm is of secondary importance in producing arterial pain. The pain of ischemia arises from chemical changes secondary to the spasm or obstruction of the artery. The pain-endings supplying arteries are sensitive to minute quantities of lactic acid, and it is possible that the pain of ischemia is due to the accumulation of this substance.[long dash]II. The peripheral anatomical paths of neurones subserving arterial pain-sensibility were traced for the arteries to the abdominal viscera [in cats and dogs]. All traverse sympathetic (or splanchnic) paths, those for the hepatic, splenic, and superior mesenteric arteries ascending in the major splanchnic nerves or the sympathetic chains to enter the cord at a thoracic level, and those for the renal arteries entering the cord at a lumbar segment after traversing a minor splanchnic nerve and a lumbar sympathetic chain. In contrast, the fibers of similar function supplying the arteries of the extremities reach the cord by way of a peripheral spinal nerve, their course cen-tralward being identical to that of the posterior root fibers subserving cutaneous sensibility. Experiments reported illustrate the importance of the sensory fibers in the sympathetic and splanchnic trunks as regards the pain-sensibility of the abdominal organs. Afferent fibers contained in the vagi and phrenic nerves seldom conduct impulses which give rise to painful sensation, the sympathetic trunks and their splanchnic branches being the true pain nerves of the abdomen.

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